1. Field of the Invention
The present invention generally relates to rotary encoders and more particularly to a rotary encoder employing a sensor head having a light emitting portion and a pair of light receiving portions respectively disposed on the both sides of the light emitting portion.
2. Description of the Prior Art
FIG. 1 shows an example of such a rotary encoder of the type as described above, in which there are provided a light output optical fiber 1 connected to a light emission element such as a light emission diode (LED)(not shown) to constitute a light emission portion, and a pair of light receiving optical fibers 2 each connected to a light receiving element such as a phototransistor (not shown) to constituted a pair of light receiving portions, the respective optical fibers 1 and 2 being bonded such that the respective tip ends of the air of light receiving optical fibers 2 are disposed on the opposite sides of the tip end of the light output optical fiber 1 to constitute a sensor head 3 with its end surface disposed in opposition to the peripheral surface of a code disk 4.
In such a rotary encoder, the light receiving element produces a high level output pulse signal when one of strip-like reflection portions 5 formed on the periphery of the code disk 4 comes in an effective reflection range formed under the bonded portion of the optical fibers 1 and 2, while produces a low level output pulse signal when one of non-reflection portions 6 formed on the periphery of the code disk 4 comes in the above-mentioned effective reflection range. The number of the thus produced high and low level pulse signals are counted to thereby detect the rotational speed of the code disk 4.
In such a rotary encoder, in order to not only detect rotational speed of the code disk 4 but detect the direction of rotation of the code disk 4 or enhance the resolution , it is preferable to provide a predetermined phase difference between the respective output waveforms of the light receiving elements connected to the pair of light receiving optical fibers 2. The sequence of generation of the respective waveforms is reversed when the code disk 4 rotates reversely, whereby the rotational direction of the code disk 4 can be detected. If the two waveforms of A- and B-phase are superimposed, with a phase difference of 90 degrees therebetween, there exist in one pitch four kinds of signal states as the combination of the phases A and B, that is a first state of (high level) and H, a second state of H and L (low level), a third state of L and H, and a fourth state L and L, so that the signal can be made to be quadruple in its state of level.
There was a disadvantage in this conventional case, however, that accuracy is required for the width of each of the optical fibers 1 and 2 in order to cause the phase difference between the two waveforms to fall within a predetermined range, resulting in complication in manufacturing.